1. Field of the Invention
The present invention relates to organophosphorus compounds comprising a polysulfide bridge, to their process of preparation and to their use as coupling agent between an inorganic filler or a metal filler and an elastomer.
2. Description of the Related Art
It is known to use coupling agents in processes targeted at reinforcing polymer matrices by inorganic particles. Mention may in particular be made of the silanes corresponding to the formula (RO)3Si(CH2)nSm(CH2)nSi(OR3) in which R=Et or Me, n=2 or 3, m=2 or 4 (DE 2141159), or in which R=Et, n=2 or 3, m=2 or 4 (DE 3311340), or in which R=Et, n=3, m=4 (DE 10015308). The improvement in the mechanical properties originates from the increase in the adhesion between the polymer matrix and the inorganic filler. These coupling agents of the silane type are particularly effective when the inorganic particles are silica or clays. However, the improvement in the mechanical properties of the matrix is smaller when the inorganic filler comprises, for example, titanium oxide or calcium carbonate and the adhesion with metal surfaces is poor.
In addition, it is known that the use of compounds of the phosphate, phosphonate or phosphinate type, as a replacement for compounds of the organosilane type, makes possible good adhesion of the phosphate compound to inorganic materials, such as metal oxides or metal surfaces. For example, G. Guerrero et al. [(2001), J. Mater. Chem, 11(12), 3161-3165] describes the grafting of phenylphosphonic acid or its ethyl or trimethylsilyl esters to alumina. G. Guerrero et al. [(2001), Chem. Mater., 13, 4367-4373] describes the grafting of phenylphosphonic acid or phenylphosphinic acid or their ethyl or trimethylsilyl esters to TiO2. The formation of phosphonic acid monolayers on metal surfaces made of steel, aluminum, copper or brass is described by J. G. Alsten [Langmuir, (1999) 15, 7605-7614]. T. Nakatsuka [Polym. Prep., Am. Chem. Soc., Div. Polym. Chem., (1983) 24(1), 202-203] describes the grafting of various phosphates, in particular (HO)2P(O)—OC8H17, to CaCO3. The use of an additive of the mercaptoalkyl-phosphonate type in elastomer compositions which comprise silica is described in U.S. Pat. No. 4,386,185; the additive is a phosphonate (RO)2P(O)-(CR′2)nSH, R being an alkyl, a cycloalkyl or an arylalkyl, R′ being H or an alkyl and n being 1 to 8. The preparation of phosphorus compounds used as catalysts is disclosed in EP-1 157 994; the compounds correspond to the formula (MO)mP(O)(OX)n(R)p[—(O)x—(Z-A)]q in which M is a monovalent cation, m+n+p+x=3, R=hydrocarbon, X=hydrocarbon or trialkylsilane and A can comprise sulfur originating, for example, from a thiol or an SO3 group.
It is known that the use of compounds of the monoalkoxytitanate type as coupling agent makes it possible to increase the amount of inorganic filler added to a thermoplastic material, without harming its fluidity (S. Monte et al., (1976) Proc., Annu. Conf., Reinf. Plast./Compos. Inst., Soc. Plast. Ind., 31, 6-E).
Furthermore, compounds of the tetrasodium 2,2′-(dithiobis)ethanephosphonate type, of use as a medicament (WO 98/14426), and dithioethers of the (HO)2P(O)—(CH2)mS2—(CH2)m—P(O)(OH)2 type, of use in reducing the toxic effect of carboplatin (WO 98/11898), are known. In addition, the use of disulfides comprising terminal groups of the ethylphosphonate type, as additive in the lubrication of fuels (GB 1 189 304), is known.
The aim of the present invention is to provide compounds of use as coupling agents between a polymer matrix and an inorganic or metal filler which exhibit improved properties, in particular with inorganic fillers other than silicas.